The Dakota Prairie Refinery in Dickinson was the first refinery to be built in the U.S. in decades.
A Houston company has applied to build another one near Berthold.
Quantum Energy and Native Son refining have applied for an air quality construction permit for a 40,000 barrel a day oil refinery.
Workers at the Health Department says the air quality permit is a key part of the permitting process.
"The key thing that we look for is to properly regulate industry. We are citizens of North Dakota and that is where our interests is. We need to make sure that that proposed facility if it's built results in cleaner air," said Jim Semerad.
Semerad says the department has just started to look over the permit.